The process of clinker /Cement production at Gujarat Sidhee Cement Ltd. Sidheegram can be briefly described as follows.
MINING: -
Drilling , blasting and surface mining to mine th ore. The rich captive mines have vast reserves of high purity lime stone expected to last for over 70 years. In these captive mines, almost all the grades of limestone is available and a very little quantity of additive is to be obtained from outside. Mining is done by surface mining technology & blasting.
CRUSHING, STACKING & RECLAIMING: -
The mined limestone is hauled through Dumpers to a rotary hammer - impact type crusher that crushes the limestone to a size up to - 75 mm (minimum 80%). Additive material is added to the crushed limestone through crusher hopper. The material is passed on to the stacker via belt conveyors, which stocks the material in longitudinal layers. The stacked material is lifted by the reclaimer, which reclaims by cutting transversely the longitudinal stacked layers ensuring perfect blending and homogenizing
RAW MEAL GRINDING: -
The desired material is drawn from lime stone reclaimer pile through the Box feeder and is fed to the vertical roller mill through air locking feeder. The vertical mill consists of a rotating table upon which 3 rotating rollers are hydraulically pressed. The material is dried and transported by the hot kiln exit gases. The size of the pulverized material is controlled by a static separator, which separates the oversized grits and sends it back on the table for further grinding. The pulverized material is transported to the C.F. Silo via energy efficient bucket elevators.
STORAGE & BLENDING: - (CAPACITY 20,000 M.T.)
The pulverized material is stored and blended in the controlled flow silo. The Blending action is achieved by extracting the material from the 7 outlets at a different rate. The extracted material is conveyed to a weighing bin where it is further blended. The operation of extraction is controlled by a PLC. The blended material is fed to the pre heater for preheating via bucket elevator.
PREHEATING, CLINKERISATION AND COOLING: -
The kiln feed from the silo; is fed into the both strings of pre heaters. Approximately 40% of the feed is given to the pre heater string where it gets preheated by the hot kiln exit gases and gets calcined up to 30% approximately. The balance 60% feed is fed to the calciner string where coal is fired in the calciner and the 30% calcined feed from the pre heater string is also added to the calciner. Here, about 90% calcinations are achieved. This 90% calcined feed is transferred to the kiln for the remaining 10 % calcinations and sintering where the flux materials and silica melt and react with lime to form four clinker constituents. This is achieved by firing coal in the rotary kiln. Kiln capacity is enhanced from 3300 TPD to 4500 TPD. The clinker coming out of the rotary kiln is at a temperature of 1300 -1400 0C and hence cooling of the same is required. This is achieved by pumping atmospheric air in the reciprocating grate cooler by 9 centrifugal fans. The clinker gets cooled and the air gets heated up and the excess air is vented out at a lower temperature. The recuperation of the heat in the cooler is in the vicinity of 65-70%.
CLINKER STORAGE & TRANSPORT: -
The clinker, which is cooled to 150o C, is stored in a silo, which has a capacity of 40,000 M.T. The clinker is transported to the silo by deep bucket conveyors. The silo for clinker is a salient feature of the plant, as the clinker does not get weathered. Another silo of 2000 M.T. Capacity is provided to store specified products/non conforming products. The clinker from the clinker silo is transported to the clinker silos of the cement mills for grinding.
CEMENT MILLS:-
The clinker is ground along with gypsum ( for OPC) and Fly ash (for PPC) at desired proportion in the highly efficient combined mills. The cement mills are two compartment tube mills. In the first compartment, the grinding is done by impact with balls and in the second compartment; it is done by attrition with small grinding media cylinders called cyllpebs. The mill is swept with air, which transports the material through the mill. The cement is pumped to the cement silos with the help of airlifts. There are four silos for cement of 5000 M.T. capacities each for storing different grades/types of cement.
PACKING PLANT: -
The packing is done by automatic rotary packers, which have a capacity of 90 TPH each. There is total No. of 5 packers. The packed bags are directly loaded into the trucks by belt conveyors. Separate system is made for loose cement loading.
RAW COAL & FINE COAL PLANT: -
Raw coal is also stacked and reclaimed by a stacker and reclaimer hence ensuring a perfectly blended Raw Coal. This is a unique feature of the plant. The Raw Coal is pulverized in a vertical roller mill, which is similar to that for the limestone.
Differential grinding of coal is done. For calciner, the coal is pulverized to a coarser size while for kiln it is ground finer and stored separately. Pneumatic screw pumps fire the coal.
CONTROL SYSTEM: -
The plant is centrally controlled except the packing plant. The control is achieved by DCS and color videography system. FUZZY LOGIC controls the kiln & cooler operation.
QUALITY CONTROL: -
The quality control is achieved with the help of an X-Ray analyzer, which gives accurate and fast results. However, a fully equipped chemical and physical laboratory is also provided to comply all National standard
QUALITY MANAGEMENT: -
The organization was first certified for ISO 9001 : 2000 Quality Management System by TUV, Germany in March 1995. We qualify under ISO 9001:2008 and ISO 14001:2004.
PRODUCTS: -
The plant produces Portland cement clinker, 33 Grade, 43 Grade, 53 Grade Ordinary Portland cement, fly ash based Portland Pozzolona cement and plans are under process to manufacturer Portland Slag cement.
MARKET: -
There is an immense market for the above products in India as well as abroad. Gujarat Sidhee Cement Ltd. is one of the leading exporters of the above products.
POLLUTION CONTROL EQUIPMENTS: -
The plant employs the relates state of art pollution control equipments like ESPS, Bag filters & Chemjets. The old generation pulse energized ESP has been modified to the latest generation ESP. The controller for the transformers has been changed and a variable inductance is provided. M/s. BHA, USA, supplied the equipment. Also the gas conditioning system supplied by M/s. Chemstrol Samil, India has been installed with this system, which conditions the gases in the down comer duct itself rather than the Gas Conditioning Tower in a conventional way.
UNIT OPERATIONS
UNIT OPERATION
DESCRIPTION
CHEMICAL REACTION
TIME REQUIRED
1) MINING
Mining of Limestone from the Mines & hauling to crusher.
No chemical reaction
---
2) CRUSHING
Crushing of the limestone from a bigger to a smaller size & adding additive material.
No chemical reaction
---
3) STACKING
Stacking of the crushed limestone in longitudinal layers to form a stockpile.
No chemical reaction
---
4) RECLAIMING
Reclaiming of the longitudinally stacked material by cutting it transversely to ensure blending.
No chemical reaction
---
5) RAW
GRINDING
The material from the pile is pulverized to a very fine powder & is stored in a Controlled Flow Silo.
No chemical reaction
---
6) PYRO
PROCESSING
The Raw Meal is extracted from the silo & it is Preheated in the PREHEATER where it gets calcined up to approx. 90% and enters the KILN for further calcinations & sintering. Sintering is the process wherein the clay components melt & form a liquid, which reacts with lime to form the potential clinker components.
ATTACHED SEPARATELY
RETENTION TIME IN KILN IS APPX. 29 MINUTES.
7) COOLING
The clinker thus formed is very hot and hence pumping cold air in the cooler through fans, which cools the clinker & heats up the combustion air, cools it. The extra cooling air is vented out through an ESP.
No chemical reaction
RETENTION TIME APPX. 20 MINUTES.
8)GRINDING
The cooled clinker is drawn from the silo & is pulverized to a very fine powder. Also, Gypsum is mixed at the inlet of the mill.
No chemical reaction
RETENTION TIME APPROX. 30 MINUTES
9) PACKING
Packing of cement form silos im bags is done by notary packers.
No chemical reaction
10) COAL
HANDLING
The coal received is stacked in piles with the help of a Stacker & is again reclaimed with Reclaimer and fed to the Coal Mill Storage Hopper.
No chemical reaction
---
11) COAL
GRINDING
Raw coal is pulv. To a fine powder in order to facilitate fast ignition of coal in a vertical mill.
No chemical reaction
---
CHEMICAL REACTIONS INVOLVED IN FORMATION OF CLINKER THE CLINKER IS MADE UP OF FOUR CONSTITUTENTS WHICH ARE AS UNDER
1
TRI-CALCIUM SILICATE (C3S)
3CaO.SiO2
2
BI-CALCIUM SILICATE (C2S)
2CaO.SiO2
3
TRI-CALCIUM SLUMINATE (C3A)
3CaO.Al203
4
TETRA CALCIUM ALUMINO FERRATE (C4AF
4CaO.Al203.Fe2O3
THE SEQUENCE OF THE CHEMICAL REACTIONS CAN BE SUMMARISED AS FOLLOWS:
S.N.
Temperature
Chemical Reaction
1
Below 800oC
Decomposition of limestone & formation of CaO.Al203 begins
2
900 - 1100oC
1) Decomposition of Calcium Carbonate is complete.
2) Formation & Decomposition of Gehlenite (2CaO+Al2O3+SiO2)
3) Formation of C3A, C4AF starts.
3
1000 - 1200oC
Formation of C2S, C3A & C4AF is nearly complete.
4
1200 - 1300oC
Liquid formation starts.
5
1200 - 1450oC
Assimilation of CaO through solid-liquid reactions & formation of C3S
